Before work began on Terminal 5, an archaeological dig was carried out on the 250-acre site. The excavation revealed the Stanwell Cursus, a 2.5-mile-long prehistoric pathway, and a horseshoe enclosure, possibly associated with the mid-winter and mid-summer solstices. Two royal, or crown, rivers were diverted during the building of Terminal 5. The Duke of Northumberland’s River was originally owned by King James I; Longford River was dug for his son, Charles I, in the early 17th century.